Apparatuses and methods for beam identification through the physical random access channel (prach) and efficient prach resource utilization

ABSTRACT

A User Equipment (UE) including a wireless transceiver and a controller is provided. The wireless transceiver performs wireless transmission and reception to and from a cellular station. The controller selects a downlink reference signal associated with a candidate beam among a plurality of downlink reference signals including Channel State Information-Reference Signal (CSI-RS) resources, Synchronization Signal (SS) blocks, or Physical Broadcast Channel (PBCH) blocks, and determines one from a plurality sets of Physical Random Access Channel (PRACH) preambles and RACH occasions for the selected downlink reference signal according to an association configured between the downlink reference signals and PRACH resources. Also, the controller uses the determined set of PRACH preamble and RACH occasion to perform a PRACH transmission to the cellular station via the wireless transceiver.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of U.S. Provisional Application No.62/475,966, filed on Mar. 24, 2017, the entirety of which isincorporated by reference herein. Also, this Application claims priorityof U.S. Provisional Application No. 62/475,970, filed on Mar. 24, 2017,the entirety of which is incorporated by reference herein.

BACKGROUND OF THE APPLICATION Field of the Application

The application generally relates to Physical Random Access Channel(PRACH) designs and, more particularly, to apparatuses and methods forbeam identification through the PRACH and efficient PRACH resourceutilization.

Description of the Related Art

The fifth generation (5G) New Radio (NR) technology is an improvementupon the fourth generation (4G) Long Term Evolution (LTE) technology,which provides extreme data speeds and capacity by utilizing higher,unlicensed spectrum bands (e.g., above 30 GHz, loosely known asmillimeter Wave (mmWave)), for wireless broadband communications. Due tothe huge path and penetration losses at millimeter wavelengths, atechnique called “beamforming” is employed and it assumes an importantrole in establishing and maintaining a robust communication link.

Beamforming generally requires one or more antenna arrays, eachcomprising a plurality of antennas. By appropriately setting antennaweights that define the contribution of each one of the antennas to atransmission or reception operation, it becomes possible to shape thesensitivity of the transmission/reception to a particularly high valuein a specific beamformed direction. By applying different antennaweights, different beam patterns can be achieved, e.g., differentdirective beams can be sequentially employed.

During a transmission (Tx) operation, beamforming may direct the signaltowards a receiver of interest. Likewise, during a reception (Rx)operation, beamforming may provide a high sensitivity in receiving asignal originating from a sender of interest. Since transmission powermay be anisotropically focused, e.g., into a solid angle of interest,beamforming may provide better link budgets due to lower required Txpower and higher received signal power, when compared to conventionalpractice, which does not employ beamforming and relies on more or lessisotropic transmission.

However, the technique mentioned above faces certain challenges. Forexample, in a multi-beam operation, the movement of a User Equipment(UE), the angular rotation of the UE, or line-of-sight blocking terrainmay cause degradation of the signal quality of the active beams. Incertain scenarios, signal quality may degrade rapidly and there may notbe enough time to switch beams, and consequently, beam failure mayoccur. Therefore, it is desirable to have a mechanism to recover frombeam failure.

Moreover, in the 5G NR technology, there are situations where PRACHpreambles may be used for uplink requests when Timing Advance (TA)command and temporary Cell Radio Network Temporary Identifier (C-RNTI)are not required to be transmitted in the responses to the uplinkrequests. Therefore, it is desirable to improve the PRACH design toadapt to such situations in a more efficient way of PRACH resourceutilization.

BRIEF SUMMARY OF THE APPLICATION

In order to solve the aforementioned problems, the present applicationproposes to recover from beam failures through the PRACH. Specifically,an association between downlink reference signals (such as the ChannelState Information-Reference Signal (CSI-RS) resources, SynchronizationSignal (SS) blocks, or Physical Broadcast Channel (PBCH) blocks) andPRACH resources (such as PRACH preambles, RACH occasions, or acombination of the above) are provided for beam identification torecover from beam failures or to facilitate handovers from one cell toanother. In addition, the present application proposes more flexiblePRACH designs for improving the efficiency of PRACH resourceutilization. Specifically, different preambles may be flexibly split forasynchronous and synchronous transmissions within a PRACH time-frequencyresource, and/or the bandwidth and/or cyclic shift used for synchronoustransmission may be reduced to be smaller than those used forasynchronous transmission.

In a first aspect of the application, a User Equipment (UE) comprising awireless transceiver and a controller is provided. The wirelesstransceiver is configured to perform wireless transmission and receptionto and from a cellular station. The controller is configured to select adownlink reference signal associated with a candidate beam among aplurality of downlink reference signals comprising Channel StateInformation-Reference Signal (CSI-RS) resources, Synchronization Signal(SS) blocks, or Physical Broadcast Channel (PBCH) blocks, determine onefrom a plurality sets of Physical Random Access Channel (PRACH)preambles and RACH occasions for the selected downlink reference signalaccording to an association configured between the downlink referencesignals and PRACH resources, and use the determined set of PRACHpreamble and RACH occasion to perform a PRACH transmission to thecellular station via the wireless transceiver.

In a second aspect of the application, a method for beam identificationthrough a PRACH, executed by a UE wirelessly connected to a cellularstation, is provided. The method for beam identification through a PRACHcomprises the steps of: selecting a downlink reference signal associatedwith a candidate beam among a plurality of downlink reference signalscomprising CSI-RS resources, SS blocks, or PBCH blocks; determining onefrom a plurality sets of PRACH preambles and RACH occasions for theselected downlink reference signal according to an associationconfigured between the downlink reference signals and PRACH resources;and using the determined set of PRACH preamble and RACH occasion toperform a PRACH transmission to the cellular station.

In a third aspect of the application, a cellular station comprising awireless transceiver and a controller is provided. The wirelesstransceiver is configured to perform wireless transmission and receptionto and from a UE. The controller is configured to receive a PRACHtransmission that utilizes a PRACH resource from the UE via the wirelesstransceiver, determine one of a plurality of downlink reference signalscomprising CSI-RS resources, SS blocks, or PBCH blocks according to anassociation configured between the downlink reference signals and thePRACH resource, and identify a candidate beam associated with thedetermined downlink reference signal.

In a fourth aspect of the application, a method for beam identificationthrough a PRACH, executed by a cellular station wirelessly connected toa UE, is provided. The method for beam identification through a PRACHcomprises the steps of: receiving a PRACH transmission that utilizes aPRACH resource from the UE; determining one of a plurality of downlinkreference signals comprising CSI-RS resources, SS blocks, or PBCH blocksaccording to an association configured between the downlink referencesignals and the PRACH resource; and identifying a candidate beamassociated with the determined downlink reference signal.

Other aspects and features of the present application will becomeapparent to those with ordinarily skill in the art upon review of thefollowing descriptions of specific embodiments of the UEs, cellularstations, and the methods for beam identification through a PRACH andfor efficient PRACH resource utilization.

BRIEF DESCRIPTION OF DRAWINGS

The application can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a block diagram of a wireless communication environmentaccording to an embodiment of the application;

FIG. 2 is a block diagram illustrating the UE 110 according to anembodiment of the application;

FIG. 3 is a block diagram illustrating a cellular station according toan embodiment of the application;

FIG. 4 is a schematic diagram illustrating the associations betweenCSI-RS resources, SS/PBCH blocks, and a plurality sets of PRACHpreambles and RACH occasions according to an embodiment of theapplication;

FIG. 5 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to an embodiment of the application;

FIG. 6 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to another embodiment of the application;

FIG. 7 is a schematic diagram illustrating the association between theCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to yet another embodiment of the application;

FIG. 8 is a schematic diagram illustrating the association between theCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to still another embodiment of the application;

FIG. 9 is a schematic diagram illustrating a joint PRACH design for beamfailure recovery and other uplink requests or indications according toan embodiment of the application;

FIG. 10 is a schematic diagram illustrating a PRACH resource utilizationfor asynchronous and synchronous transmissions according to anembodiment of the application;

FIG. 11 is a schematic diagram illustrating the PRACH preamblebandwidths for asynchronous and synchronous transmissions according toan embodiment of the application; and

FIG. 12 is a schematic diagram illustrating a PRACH resource utilizationfor asynchronous and synchronous transmissions according to anotherembodiment of the application.

DETAILED DESCRIPTION OF THE APPLICATION

The following description is made for the purpose of illustrating thegeneral principles of the application and should not be taken in alimiting sense. It should be understood that the embodiments may berealized in software, hardware, firmware, or any combination thereof.The terms “comprises,” “comprising,” “includes” and/or “including,” whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

FIG. 1 is a block diagram of a wireless communication environmentaccording to an embodiment of the application. The wirelesscommunication environment 100 includes a User Equipment (UE) 110 and a5G NR network 120, wherein the UE 110 may initiate a random accessprocedure for beam failure recovery, beam handover, or uplink request,and may be wirelessly connected to the 5G NR network 120 for obtainingmobile services.

The UE 110 may be a feature phone, a smartphone, a panel PersonalComputer (PC), a laptop computer, or any wireless communication devicesupporting the cellular technology (i.e., the 5G NR technology) utilizedby the 5G NR network 120. Particularly, the wireless communicationdevice employs the beamforming technique for wireless transmissionand/or reception.

The 5G NR network 120 includes a Radio Access Network (RAN) 121 and aNext Generation Core Network (NG-CN) 122.

The RAN 121 is responsible for processing radio signals, terminatingradio protocols, and connecting the UE 110 with the NG-CN 122. Inaddition, the RAN 121 is responsible for periodically broadcasting theminimum SI, and providing the other SI by periodic broadcasting or atthe request of the UE 110. The RAN 121 may include one or more cellularstations, such as gNBs, which support high frequency bands (e.g., above24 GHz), and each gNB may further include one or more TransmissionReception Points (TRPs), wherein each gNB or TRP may be referred to as a5G cellular station. Some gNB functions may be distributed acrossdifferent TRPs, while others may be centralized, leaving the flexibilityand scope of specific deployments to fulfill the requirements forspecific cases.

The NG-CN 122 generally consists of various network functions, includingAccess and Mobility Function (AMF), Session Management Function (SMF),Policy Control Function (PCF), Application Function (AF), AuthenticationServer Function (AUSF), User Plane Function (UPF), and User DataManagement (UDM), wherein each network function may be implemented as anetwork element on a dedicated hardware, or as a software instancerunning on a dedicated hardware, or as a virtualized functioninstantiated on an appropriate platform, e.g., a cloud infrastructure.

The AMF provides UE-based authentication, authorization, mobilitymanagement, etc. The SMF is responsible for session management andallocates Internet Protocol (IP) addresses to UEs. It also selects andcontrols the UPF for data transfer. If a UE has multiple sessions,different SMFs may be allocated to each session to manage themindividually and possibly provide different functions per session. TheAF provides information on the packet flow to PCF responsible for policycontrol in order to support Quality of Service (QoS). Based on theinformation, the PCF determines policies about mobility and sessionmanagement to make the AMF and the SMF operate properly. The AUSF storesdata for authentication of UEs, while the UDM stores subscription dataof UEs.

It should be understood that the 5G NR network 120 depicted in FIG. 1 isfor illustrative purposes only and is not intended to limit the scope ofthe application. The application may also be applied to other cellulartechnologies, such as a future enhancement of the 5G NR technology.

FIG. 2 is a block diagram illustrating the UE 110 according to anembodiment of the application. The UE 110 includes a wirelesstransceiver 10, a controller 20, a storage device 30, a display device40, and an Input/Output (I/O) device 50.

The wireless transceiver 10 is configured to perform wirelesstransmission and reception to and from the RAN 121. Specifically, thewireless transceiver 10 includes a Radio Frequency (RF) device 11, abaseband processing device 12, and antenna(s) 13, wherein the antenna(s)13 may include one or more antennas for beamforming. The basebandprocessing device 12 is configured to perform baseband signal processingand control the communications between subscriber identity card(s) (notshown) and the RF device 11. The baseband processing device 12 maycontain multiple hardware components to perform the baseband signalprocessing, including Analog-to-Digital Conversion(ADC)/Digital-to-Analog Conversion (DAC), gain adjusting,modulation/demodulation, encoding/decoding, and so on. The RF device 11may receive RF wireless signals via the antenna(s) 13, convert thereceived RF wireless signals to baseband signals, which are processed bythe baseband processing device 12, or receive baseband signals from thebaseband processing device 12 and convert the received baseband signalsto RF wireless signals, which are later transmitted via the antenna(s)13. The RF device 11 may also contain multiple hardware devices toperform radio frequency conversion. For example, the RF device 11 mayinclude a mixer to multiply the baseband signals with a carrieroscillated in the radio frequency of the supported cellulartechnologies, wherein the radio frequency may be any radio frequency(e.g., 30 GHz-300 GHz for mmWave) utilized in the 5G NR technology, oranother radio frequency, depending on the cellular technology in use.

The controller 20 may be a general-purpose processor, a Micro ControlUnit (MCU), an application processor, a Digital Signal Processor (DSP),or the like, which includes various circuits for providing the functionsof data processing and computing, controlling the wireless transceiver10 for wireless communications with the RAN 121, storing and retrievingdata (e.g., program code) to and from the storage device 30, sending aseries of frame data (e.g. representing text messages, graphics, images,etc.) to the display device 40, and receiving signals from the I/Odevice 50. In particular, the controller 20 coordinates theaforementioned operations of the wireless transceiver 10, the storagedevice 30, the display device 40, and the I/O device 50 for performingthe method for beam identification through the PRACH and the method forefficient PRACH utilization.

In another embodiment, the controller 20 may be incorporated into thebaseband processing device 12, to serve as a baseband processor.

As will be appreciated by persons skilled in the art, the circuits ofthe controller 20 will typically include transistors that are configuredin such a way as to control the operation of the circuits in accordancewith the functions and operations described herein. As will be furtherappreciated, the specific structure or interconnections of thetransistors will typically be determined by a compiler, such as aRegister Transfer Language (RTL) compiler. RTL compilers may be operatedby a processor upon scripts that closely resemble assembly languagecode, to compile the script into a form that is used for the layout orfabrication of the ultimate circuitry. Indeed, RTL is well known for itsrole and use in the facilitation of the design process of electronic anddigital systems.

The storage device 30 is a non-transitory machine-readable storagemedium, including a memory, such as a FLASH memory or a Non-VolatileRandom Access Memory (NVRAM), or a magnetic storage device, such as ahard disk or a magnetic tape, or an optical disc, or any combinationthereof for storing instructions and/or program code of applications,communication protocols, and/or the methods for beam identificationthrough the PRACH and for efficient PRACH utilization.

The display device 40 may be a Liquid-Crystal Display (LCD), aLight-Emitting Diode (LED) display, or an Electronic Paper Display(EPD), etc., for providing a display function. Alternatively, thedisplay device 40 may further include one or more touch sensors disposedthereon or thereunder for sensing touches, contacts, or approximationsof objects, such as fingers or styluses.

The I/O device 50 may include one or more buttons, a keyboard, a mouse,a touch pad, a video camera, a microphone, and/or a speaker, etc., toserve as the Man-Machine Interface (MIMI) for interaction with users.

It should be understood that the components described in the embodimentof FIG. 2 are for illustrative purposes only and are not intended tolimit the scope of the application. For example, the UE 110 may includemore components, such as a power supply, or a Global Positioning System(GPS) device, wherein the power supply may be a mobile/replaceablebattery providing power to all the other components of the UE 110, andthe GPS device may provide the location information of the UE 110 foruse of some location-based services or applications.

FIG. 3 is a block diagram illustrating a cellular station according toan embodiment of the application. The cellular station may be a 5Gcellular station, such as a gNB or TRP. The cellular station includes awireless transceiver 60, a controller 70, a storage device 80, and awired interface 90.

The wireless transceiver 60 is configured to perform wirelesstransmission and reception to and from the UE 110. Specifically, thewireless transceiver 60 includes an RF device 61, a baseband processingdevice 62, and antenna(s) 63, wherein the antenna(s) 63 may include oneor more antennas for beamforming. The functions of the RF device 61, thebaseband processing device 62, and the antenna(s) 63 are similar tothose of the RF device 11, the baseband processing device 12, and theantenna(s) 13 as described in the embodiment of FIG. 2, and thus, thedetailed description is not repeated herein for brevity.

The controller 70 may be a general-purpose processor, an MCU, anapplication processor, a DSP, or the like, which includes variouscircuits for providing the functions of data processing and computing,controlling the wireless transceiver 60 for wireless communications withthe UE 110, storing and retrieving data (e.g., program code) to and fromthe storage device 80, and sending/receiving messages to/from othernetwork entities (e.g., other cellular stations in the RAN 121 or othernetwork entities in the NG-CN 122) through the wired interface 90. Inparticular, the controller 70 coordinates the aforementioned operationsof the wireless transceiver 60, the storage device 80, and the wiredinterface 90 to perform the method for beam identification through thePRACH and the method for efficient PRACH utilization.

In another embodiment, the controller 70 may be incorporated into thebaseband processing device 62, to serve as a baseband processor.

As will be appreciated by persons skilled in the art, the circuits ofthe controller 70 will typically include transistors that are configuredin such a way as to control the operation of the circuits in accordancewith the functions and operations described herein. As will be furtherappreciated, the specific structure or interconnections of thetransistors will typically be determined by a compiler, such as an RTLcompiler. RTL compilers may be operated by a processor upon scripts thatclosely resemble assembly language code, to compile the script into aform that is used for the layout or fabrication of the ultimatecircuitry. Indeed, RTL is well known for its role and use in thefacilitation of the design process of electronic and digital systems.

The storage device 80 may be a memory, such as a FLASH memory or anNVRAM, or a magnetic storage device, such as a hard disk or a magnetictape, or an optical disc, or any combination thereof for storinginstructions and/or program code of applications, communicationprotocols, and/or the methods for beam identification through the PRACHand for efficient PRACH utilization.

The wired interface 90 is responsible for providing wired communicationswith other network entities, such as other cellular stations in the RAN121, or other network entities in the NG-CN 122. The wired interface 90may include a cable modem, an Asymmetric Digital Subscriber Line (ADSL)modem, a Fiber-Optic Modem (FOM), and/or an Ethernet interface.

It should be understood that the components described in the embodimentof FIG. 3 are for illustrative purposes only and are not intended tolimit the scope of the application. For example, the cellular stationmay further include other functional devices, such as a display device(e.g., LCD, LED display, or EPD, etc.), an I/O device (e.g., button,keyboard, mouse, touch pad, video camera, microphone, speaker, etc.),and/or a power supply, etc.

Please note that, in the present application, an association between thedownlink reference signals and the PRACH preambles and RACH occasions(e.g., time-frequency resources) is configured for indicating thedownlink reference signal selected by UE to the cellular station when aPRACH preamble is transmitted by the UE and detected by the cellularstation. A RACH occasion is defined as the time-frequency resource onwhich a PRACH message 1 is transmitted using the configured PRACHpreamble format with a single particular TX beam. Furthermore, the usageof PRACH transmission includes new candidate beam identification torecover from beam failures or to facilitate handovers from one cell toanother. When a beam failure occurs or a cell handover is triggered, adownlink reference signal associated with a candidate beam will beselected among the set of downlink reference signals associated with allbeams, wherein the set of downlink reference signals includes CSI-RSresources, SS blocks, or PBCH blocks, or any combination thereof. Basedon the association, the PRACH preambles and RACH occasions correspondingto the newly selected downlink reference signal (i.e., CSI-RS resourceor SS/PBCH block) of the candidate beam may be determined, and the UEmay transmit a random access preamble according to the determined PRACHpreamble on the determined RACH occasion to the gNB. On the other hand,when receiving the random access preamble, the gNB knows that a beamfailure occurs or a cell handover is triggered, and knows which beam isthe new candidate beam selected by the UE, when receiving the randomaccess preamble, based on the association.

FIG. 4 is a schematic diagram illustrating the associations betweenCSI-RS resources, SS/PBCH blocks, and a plurality sets of PRACHpreambles and RACH occasions according to an embodiment of theapplication.

In this embodiment, the beam width of each CSI-RS resource issubstantially the same as the beam width of each SS/PBCH block, andthus, the association between CSI-RS resources and PRACH preambles andRACH occasions can be the same as the association between the SS/PBCHblocks and the PRACH preambles and RACH occasions. That is, theassociation associates one CSI-RS resource or SS/PBCH block to one setof PRACH preambles and RACH occasions.

As shown in FIG. 4, the first SS/PBCH block and the first CSI-RSresource are corresponding to the first set of PRACH preambles and RACHoccasions according to the associations, and thus, the beams used forthe first SS/PBCH block and the first CSI-RS resource are correspondingto the beam used for the first set of PRACH preambles and RACHoccasions.

Likewise, the second SS/PBCH block and the second CSI-RS resource arecorresponding to the second set of PRACH preambles and RACH occasionsaccording to the associations, and thus, the beams used for the secondSS/PBCH block and the second CSI-RS resource are corresponding to thebeam used for the second set of PRACH preambles and RACH occasions. Thethird blocks/PBCH block and the third CSI-RS resource are correspondingto the third set of PRACH preambles and RACH occasions according to theassociations, and thus, the beams used for the third SS/PBCH block andthe third CSI-RS are corresponding to the beam used for the third set ofPRACH preambles and RACH occasions. The fourth SS/PBCH block and thefourth CSI-RS resource are corresponding to the fourth set of PRACHpreambles and RACH occasions according to the associations, and thus,the beams used for the fourth SS/PBCH block and the fourth CSI-RSresource are corresponding to the beam used for the fourth set of PRACHpreambles and RACH occasions.

Please note that, in another embodiment, the associations are configuredbetween CSI-RS resources and the PRACH preambles. For example, the firstCSI-RS resource is associated with the first set of PRACH preamble(s),the second CSI-RS resource is associated with the second set of PRACHpreamble(s), and so on. In another embodiment, the associations areconfigured between SS/PBCH blocks and the PRACH preambles. For example,the first SS/PBCH block is associated with the first set of PRACHpreamble(s), the second SS/PBCH block is associated with the second setof PRACH preamble(s), and so on. In another embodiment, the associationsare configured between CSI-RS resources and the RACH occasions. Forexample, the first CSI-RS resource is associated with the first RACHoccasion(s), the second CSI-RS resource is associated with the secondRACH occasion(s), and so on. In another embodiment, the associations areconfigured between SS/PBCH blocks and the RACH occasions. For example,the first SS/PBCH block is associated with the first RACH occasion(s),the second SS/PBCH block is associated with the second RACH occasion(s),and so on. In another embodiment, the associations are configuredbetween CSI-RS resources and both the PRACH preambles and the RACHoccasions. For example, the first CSI-RS resource is associated with thefirst set of PRACH preamble(s) and the first RACH occasion(s), thesecond CSI-RS resource is associated with the second set of PRACHpreamble(s) and the second RACH occasion(s), and so on. In anotherembodiment, the associations are configured between SS/PBCH blocks andboth the PRACH preambles and the RACH occasions. For example, the firstSS/PBCH block is associated with the first set of PRACH preamble(s) andthe first RACH occasion(s), the second SS/PBCH block is associated withthe second set of PRACH preamble(s) and the second RACH occasion(s), andso on.

That is to say, for purposes not limited to beam failure recovery, newbeam identification, and handover, there are associations configuredbetween (1) the CSI-RS resources and RACH resources including preambles,occasions (e.g., time-frequency resources), or a combination thereof,(2) the SS/PBCH blocks and RACH resources including preambles, occasions(e.g., time-frequency resources), or a combination thereof, or (3) theCSI-RS resources and the SS/PBCH blocks and RACH resources includingpreambles, occasions (e.g., time-frequency resources), or a combinationthereof.

FIG. 5 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to an embodiment of the application.

In this embodiment, the beam width of each CSI-RS resources is narrowerthan the beam width of the downlink reference signals (e.g. SS/PBCHblocks) that PRACH preambles and RACH occasions are configured to beassociated with. Specifically, the beam width of each CSI-RS resourcesis substantially half the beam width of the downlink reference signalsthat PRACH preambles and RACH occasions are associated with. That is,the association associates multiple (e.g., two) CSI-RS resources to oneset of PRACH preambles and RACH occasions.

As shown in FIG. 5, the first and second CSI-RS resources arecorresponding to the first set of PRACH preambles and RACH occasionsaccording to the association, and thus, the beams used for the first andsecond CSI-RS resources are corresponding to the beam used for the firstset of PRACH preambles and RACH occasions. The third and fourth CSI-RSresources are corresponding to the second set of PRACH preambles andRACH occasions according to the association, and thus, the beams usedfor the third and fourth CSI-RS resources are corresponding to the beamused for the second set of PRACH preambles and RACH occasions. The fifthand sixth CSI-RS resources are corresponding to the third set of PRACHpreambles and RACH occasions according to the association, and thus, thebeams used for the fifth and sixth CSI-RS resources are corresponding tothe beam used for the third set of PRACH preambles and RACH occasions.The seventh and eighth CSI-RS resources are corresponding to the fourthset of PRACH preambles and RACH occasions according to the association,and thus, the beams used for the seventh and eighth CSI-RS resources arecorresponding to the beam used for the fourth set of PRACH preambles andRACH occasions.

In another embodiment, the associations are configured between CSI-RSresources and the PRACH preambles. For example, the first and the secondCSI-RS resources are associated with the first set of PRACH preamble(s),the third and fourth CSI-RS resources are associated with the second setof PRACH preamble(s), and so on. In another embodiment, the associationsare configured between CSI-RS resources and the RACH occasions. Forexample, the first and second CSI-RS resources are associated with thefirst RACH occasion(s), the third and fourth CSI-RS resources areassociated with the second RACH occasion(s), and so on.

That is to say, for purposes not limited to beam failure recovery, newbeam identification and hangover, there are associations configuredbetween the CSI-RS resources and RACH resources including preambles,occasions (e.g., time-frequency resources), or a combination thereof.

The advantage of this kind of association (i.e., the mapping of multipleCSI-RS resources to one set of PRACH preambles and RACH occasions) isthat fewer PRACH resources are required. The disadvantages of this kindof association are that the new beam information is only partiallyconveyed through the first step of a random access procedure and widerbeams are used for the messages in the third step (i.e., schedulingrequest) and the fourth step (i.e., contention resolution) of acontention-based random access procedure. However, the conveyance of thenew beam information may be completed through the message of the thirdstep (i.e., uplink transmission) of a contention-based random accessprocedure.

FIG. 6 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality sets of PRACH preambles and RACHoccasions according to another embodiment of the application.

In this embodiment, the association associates the CSI-RS resources tothe sets of PRACH preambles and RACH occasions by Code DivisionMultiplexing (CDM).

As shown in FIG. 6, there are at least two sets of PRACH preambleswithin each RACH occasion, wherein preambles from the two PRACH preamblesets may be differentiated at the code domain (i.e., preamble domain).

The first and second CSI-RS resources are corresponding to the first andsecond PRACH preamble sets within the first RACH occasion, respectively.The third and fourth CSI-RS resources are corresponding to the first andsecond PRACH preamble sets within the second RACH occasion,respectively. The fifth and sixth CSI-RS resources are corresponding tothe first and second PRACH preamble sets within the third RACH occasion,respectively. The seventh and eighth CSI-RS resources are correspondingto the first and second PRACH preamble sets within the fourth RACHoccasion, respectively.

FIG. 7 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality of PRACH preambles and RACH occasionsaccording to yet another embodiment of the application.

In this embodiment, the association associates one CSI-RS resource toone set of RACH occasions by Frequency Division Multiplexing (FDM).

As shown in FIG. 7, there are two RACH occasions within each PRACH timeperiod, wherein the two RACH occasions may be differentiated at thefrequency domain.

The first and second CSI-RS resources are corresponding to the first andsecond RACH occasions within the first PRACH time period, respectively.The third and fourth CSI-RS resources are corresponding to the first andsecond RACH occasions within the second PRACH time period, respectively.The fifth and sixth CSI-RS resources are corresponding to the first andsecond RACH occasions within the third PRACH time period, respectively.The seventh and eighth CSI-RS resources are corresponding to the firstand second RACH occasions within the fourth PRACH time period,respectively.

FIG. 8 is a schematic diagram illustrating the association betweenCSI-RS resources and a plurality of PRACH preambles and RACH occasionsaccording to still another embodiment of the application.

In this embodiment, the association associates one CSI-RS resource toone set of PRACH preambles and RACH occasions by Time DivisionMultiplexing (TDM).

As shown in FIG. 8, the four RACH occasions are duplicated at the timedomain, wherein each of the eight RACH occasions may be differentiatedat the time domain with the same frequency range.

The first and second CSI-RS resources are corresponding to the firstRACH occasion within the first span of the time domain and the firstRACH occasion within the second span of the time domain, respectively.The third and fourth CSI-RS resources are corresponding to the secondRACH occasion within the first span of the time domain and the secondRACH occasion within the second span of the time domain, respectively.The fifth and sixth CSI-RS resources are corresponding to the third RACHoccasion within the first span of the time domain and the third RACHoccasion within the second span of the time domain, respectively. Theseventh and eighth CSI-RS resources are corresponding to the fourth RACHoccasion within the first span of the time domain and the fourth RACHoccasion within the second span of the time domain, respectively.

The advantages of the associations in FIGS. 6 to 8 are that the new beaminformation may be fully conveyed through the first step of a randomaccess procedure and narrower beams may be used for the messages of thethird step (i.e., uplink transmission) and fourth step (e.g., contentionresolution) of a contention-based random access procedure (narrower beammay render better spectral efficiency). Please note that the associationbetween downlink reference signals (i.e., CSI-RS resources and/orSS/PBCH blocks) and a plurality sets of PRACH preambles and/or RACHoccasions can be based on any combination of the above mentioned CDM,FDM, and TDM methods.

FIG. 9 is a schematic diagram illustrating a joint PRACH design for beamfailure recovery and other uplink requests or indication according to anembodiment of the application.

In this embodiment, a dedicated preamble may be allocated for beamfailure recovery and other uplink requests or indication, such asscheduling request or an acknowledgement (ACK) or non-acknowledgement(NACK) signal.

Specifically, when transmitted on one of the serving beam(s) (denoted asBeam1 in FIG. 9), the dedicated preamble serves as a scheduling requestor an ACK/NACK signal. When transmitted on one of the non-serving beams(denoted as Beam2 to Beam4 in FIG. 9), the dedicated preamble serves asa request for beam failure recovery.

As shown in FIG. 9, the preamble may serve as a scheduling request whenit is transmitted on Beam1 (i.e., the serving beam), and may serve as arequest for beam failure recovery when it is transmitted on Beam 4(i.e., a non-serving beam).

Please note that, in the present application, more flexible PRACHdesigns for improving the efficiency of PRACH resource utilization areproposed. For example, different preambles may be flexibly split forasynchronous and synchronous transmissions within a RACH occasion,and/or the bandwidth by utilizing a preamble format with a smallersequence length or by configuring a smaller sub-carrier spacing, and/orcyclic shift used for synchronous transmission may be reduced to besmaller than those used for asynchronous transmission.

FIG. 10 is a schematic diagram illustrating a PRACH resource utilizationfor asynchronous and synchronous transmissions according to anembodiment of the application.

As shown in FIG. 10, there are four different PRACH configurations forthe same PRACH time-frequency resource. In the first PRACH configuration(denoted as Config.0 in FIG. 10), the preambles generated using allZadoff-Chu (ZC) roots are for asynchronous transmissions, and the PRACHresource blocks for asynchronous transmissions using different preamblesare denoted as Async.B1 to Async.B4.

In the rest of the PRACH configurations (denoted as Config.1 to Config.3in FIG. 10), the preambles generated using all ZC roots are split forasynchronous and synchronous transmissions within the same PRACHtime-frequency resource, and the PRACH resource blocks for asynchronoustransmissions using different preambles are denoted as Async.B5 toAsync.B6, while the PRACH resource blocks for synchronous transmissionsusing different preambles are denoted as Sync.B1 to Sync.B2.

An example of the preambles and the number of ZC roots used forasynchronous and synchronous transmissions in each PRACH configurationis provided in table 1 as follows (assuming that the PRACH SubcarrierSpacing (SCS) is 30 KHz, and the Inter-Site Distance (ISD) is 500meters).

TABLE 1 # of # of preambles for # of ZC preambles for # of ZC rootsAsyn. Tx roots for Syn. Tx Configuration # for Asyn. Tx (upper bound)Syn. Tx (upper bound) 0 6 60 0 0 1 5 50 1 33 2 4 40 2 66 3 3 30 3 99

For uplink synchronous PRACH attempts or PRACH attempts that are notfollowed by Physical Uplink Control Channel (PUCCH) or Physical UplinkShared Channel (PUSCH) transmissions, the gNB does not need to includethe Timing Advance (TA) command and the temporary Cell Radio NetworkTemporary Identifier (C-RNTI) in the response to these PRACH attempts.

FIG. 11 is a schematic diagram illustrating the PRACH preamblebandwidths for asynchronous and synchronous transmissions according toan embodiment of the application.

The PRACH time-frequency resource used for asynchronous transmissions isshown on the left side of FIG. 11, in which the number of ZC roots is 8and the length of preamble sequences is 839. The PRACH time-frequencyresource used for synchronous transmissions (where TA estimation is notrequired) is shown on the right side of FIG. 11, in which the number ofZC roots is 2 and the length of preamble sequences is 139. That is, thePRACH preamble bandwidth for synchronous transmission is narrower thanthe PRACH preamble bandwidth for asynchronous transmission. In otherwords, the PRACH bandwidth can be reduced by configuring a preambleformat with a smaller sequence length or by configuring a smallersub-carrier spacing.

Due to the fact that the preamble sequence is shortened and the numberof ZC roots within the PRACH time-frequency resource for synchronoustransmissions is reduced, the Multiple Access Interference (MAI) fromother root sequences may be reduced.

In addition, since TA estimation is not required for synchronous PRACHtransmissions, the cyclic shift does not need to cover the round-trippropagation delay, and the cyclic shift applied for generating thepreambles may be reduced.

Alternatively, the PRACH preamble bandwidth and the cyclic shift usedfor synchronous transmission may be reduced to be smaller than thoseused for asynchronous transmission.

FIG. 12 is a schematic diagram illustrating a PRACH resource utilizationfor asynchronous and synchronous transmissions according to anotherembodiment of the application.

The PRACH time-frequency resource for asynchronous transmissions isshown on the left side of FIG. 12, in which the number of ZC roots is 8,the length of preamble sequences is 839, and the cyclic shift is 9. ThePRACH time-frequency resources for synchronous transmissions are shownon the right side of FIG. 12, in which the number of ZC roots is 2, thelength of preamble sequences is 139, and the cyclic shift is 2.

As shown in FIG. 12, there may be multiple PRACH time-frequencyresources for synchronous transmissions allocated within the same PRACHtime period. Advantageously, this allocation may achieve the targetpreamble opportunities without introducing severe MAI from other rootsequences.

In view of the forgoing embodiments, it will be appreciated that thepresent application realizes beam failure recovery or beam handoverthrough the PRACH, by providing an association between the downlinkreference signals (e.g., CSI-RS resources, and/or SS/PBCH blocks) andthe PRACH resources (including the sets of PRACH preambles, RACHoccasions, or any combination thereof) for beam identification. Also,the present application realizes more flexible PRACH designs, byallowing different preambles to be flexibly split for asynchronous andsynchronous transmissions within a PRACH time-frequency resource, and/orreducing the bandwidth and/or cyclic shift used for synchronoustransmission to be smaller than those used for asynchronoustransmission. Advantageously, spectral efficiency and the efficiency ofPRACH utilization may be significantly improved.

While the application has been described by way of example and in termsof preferred embodiment, it should be understood that the application isnot limited thereto. Those who are skilled in this technology can stillmake various alterations and modifications without departing from thescope and spirit of this application. Therefore, the scope of thepresent application shall be defined and protected by the followingclaims and their equivalents.

Use of ordinal terms such as “first”, “second”, etc., in the claims tomodify a claim element does not by itself connote any priority,precedence, or order of one claim element over another or the temporalorder in which acts of a method are performed, but are used merely aslabels to distinguish one claim element having a certain name fromanother element having the same name (but for use of the ordinal term)to distinguish the claim elements.

What is claimed is:
 1. A User Equipment (UE), comprising: a wirelesstransceiver, configured to perform wireless transmission and receptionto and from a cellular station; and a controller, configured to select adownlink reference signal associated with a candidate beam among aplurality of downlink reference signals comprising Channel StateInformation-Reference Signal (CSI-RS) resources, Synchronization Signal(SS) blocks, or Physical Broadcast Channel (PBCH) blocks, determine onefrom a plurality sets of Physical Random Access Channel (PRACH)preambles and RACH occasions for the selected downlink reference signalaccording to an association configured between the downlink referencesignals and PRACH resources, and use the determined set of PRACHpreamble and RACH occasion to perform a PRACH transmission to thecellular station via the wireless transceiver.
 2. The UE of claim 1,wherein the candidate beam is used for beam failure recovery or for ahandover from a cell to another cell.
 3. The UE of claim 1, wherein thePRACH resources comprises the PRACH preambles, the RACH occasions, or acombination thereof, and the association is configured between thedownlink reference signals and the PRACH preambles, the RACH occasions,or a combination thereof.
 4. The UE of claim 1, wherein, when the PRACHtransmission comprises transmitting a first PRACH preamble using a firstRACH occasion which corresponds to the selected downlink referencesignal, the first PRACH preamble is used for one purpose; and when thePRACH transmission comprises transmitting the first PRACH preamble usinga second RACH occasion which corresponds to another downlink referencesignal, the first PRACH preamble is used for another purpose.
 5. The UEof claim 4, wherein, when the first PRACH preamble is transmitted on aserving beam, the first PRACH preamble serves as a scheduling request oran acknowledgement (ACK) or non-acknowledgement (NACK) signal, and whenthe first PRACH preamble is transmitted on the candidate beam, the firstPRACH preamble serves as a request for beam failure recovery.
 6. The UEof claim 1, wherein the association configured between the downlinkreference signals and the PRACH resources associates one CSI-RSresource, SS block, or PBCH block to one set of PRACH resource, orassociates multiple CSI-RS resources, SS blocks, or PBCH blocks to oneset of PRACH resource.
 7. The UE of claim 6, wherein, when theassociation configured between the downlink reference signals and thePRACH resources associates multiple CSI-RS resources, SS blocks, or PBCHblocks to one set of PRACH resource, the controller is furtherconfigured to transmit an uplink transmission to the cellular stationvia the wireless transceiver for identifying which one of the multipleCSI-RS resources, SS blocks, or PBCH blocks is associated with thecandidate beam.
 8. The UE of claim 6, wherein the association configuredbetween the downlink reference signals and the PRACH resourcesassociates one CSI-RS resource, SS block, or PBCH block to one set ofPRACH resource, by at least one of: Code Division Multiplexing (CDM),Frequency Division Multiplexing (FDM), and Time Division Multiplexing(TDM).
 9. A method for beam identification through a PRACH, executed bya UE wirelessly connected to a cellular station, the method comprising:selecting a downlink reference signal associated with a candidate beamamong a plurality of downlink reference signals comprising CSI-RSresources, SS blocks, or PBCH blocks; determining one from a pluralitysets of PRACH preambles and RACH occasions for the selected downlinkreference signal according to an association configured between thedownlink reference signals and PRACH resources; and using the determinedset of PRACH preamble and RACH occasion to perform a PRACH transmissionto the cellular station.
 10. The method of claim 9, wherein thecandidate beam is used for beam failure recovery or for a handover froma cell to another cell.
 11. The method of claim 9, wherein the PRACHresources comprises the PRACH preambles, the RACH occasions, or acombination thereof, and the association is configured between thedownlink reference signals and the PRACH preambles, the RACH occasions,or a combination thereof.
 12. The method of claim 9, wherein, when thePRACH transmission comprises transmitting a first PRACH preamble using afirst RACH occasion which corresponds to the selected downlink referencesignal, the first PRACH preamble is used for one purpose; and when thePRACH transmission comprises transmitting the first PRACH preamble usinga second RACH occasion which corresponds to another downlink referencesignal, the first PRACH preamble is used for another purpose.
 13. Themethod of claim 12, wherein, when the first PRACH preamble istransmitted on a serving beam, the first PRACH preamble serves as ascheduling request or an ACK or NACK signal, and when the first PRACHpreamble is transmitted on the candidate beam, the first PRACH preambleserves as a request for beam failure recovery.
 14. The method of claim9, wherein the association configured between the downlink referencesignals and the PRACH resources associates one CSI-RS resource, SSblock, or PBCH block to one set of PRACH resource, or associatesmultiple CSI-RS resources, SS blocks, or PBCH blocks to one set of PRACHresource.
 15. The method of claim 14, further comprising: when theassociation configured between the downlink reference signals and thePRACH resources associates multiple CSI-RS resources, SS blocks, or PBCHblocks to one set of PRACH resource, transmitting an uplink transmissionto the cellular station for identifying which one of the multiple CSI-RSresource, SS blocks, or PBCH blocks is associated with the candidatebeam.
 16. The method of claim 9, wherein the association configuredbetween the downlink reference signals and the PRACH resourcesassociates one CSI-RS resource, SS block, or PBCH block to one set ofPRACH resource, by at least one of: CDM, FDM, and TDM.
 17. A cellularstation, comprising: a wireless transceiver, configured to performwireless transmission and reception to and from a UE; and a controller,configured to receive a PRACH transmission which utilizes a PRACHresource from the UE via the wireless transceiver, determine one of aplurality of downlink reference signals comprising CSI-RS resources, SSblocks, or PBCH blocks according to an association configured betweenthe downlink reference signals and the PRACH resource, and identify acandidate beam associated with the determined downlink reference signal.18. The cellular station of claim 17, wherein the candidate beam isidentified for beam failure recovery, or for a handover from a cell toanother cell.
 19. The cellular station of claim 17, wherein the PRACHtransmission comprising a PRACH preamble transmitted on a RACH occasion,and the association is configured between the downlink reference signalsand the PRACH preamble, the RACH occasion, or a combination thereof. 20.The cellular station of claim 17, wherein the association configuredbetween the downlink reference signals and the PRACH resource associatesone CSI-RS resource, SS block, or PBCH block to one set of PRACHresource, or associates multiple CSI-RS resources, SS blocks, or PBCHblocks to one set of PRACH resource.
 21. A method for beamidentification through a PRACH, executed by a cellular stationwirelessly connected to a UE, the method comprising: receiving a PRACHtransmission which utilizes a PRACH resource from the UE; determiningone of a plurality of downlink reference signals comprising CSI-RSresources, SS blocks, or PBCH blocks according to an associationconfigured between the downlink reference signals and the PRACHresource; and identifying a candidate beam associated with thedetermined downlink reference signal.
 22. The method of claim 21,wherein the candidate beam is identified for beam failure recovery, orfor a handover from a cell to another cell.
 23. The method of claim 21,wherein the PRACH transmission comprising a PRACH preamble transmittedon a RACH occasion, and the association is configured between thedownlink reference signals and the PRACH preamble, the RACH occasion, ora combination thereof.
 24. The method of claim 21, wherein theassociation configured between the downlink reference signals and thePRACH resource associates one CSI-RS resource, SS block, or PBCH blockto one set of PRACH resource, or associates multiple CSI-RS resources,SS blocks, or PBCH blocks to one set of PRACH resource.